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    <script>
        //1.双重for循环里，外层循环一次，里面的循环执行全部
        for (var i = 1; i <= 4; i++) {
            console.log('这是外循环第' + i + '次');
            for (var j = 1; j <= 3; j++) {
                console.log('这是内循环第' + j + '次');
            }
        }
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